Electron delocalisation during oxidation-reduction cycle of FAD: design and fabrication of a coenzyme immobilized bioanode

Abstract

A biochemical fuel cell is an electrochemical power generation device that converts the chemical energy of a fuel (alcohol, glucose, hydrocarbons, etc) directly into electrical energy through enzyme-catalysed oxidation-reduction reactions. These systems possess several advantages over the conventional processes and are ideal for rural electrification in conjunction with biogas plants. The major bottleneck in the design of such power sources is the electron transport from the substrate to the electrode. Biochemical systems which use coenzymes such asfad ornad seem to be the most promising in circumventing these difficulties. We have made systematic molecular orbital studies of the electron-flow diagrams of riboflavin during its oxidation-reduction cycle and it is possible to obtain very efficient electron transport from the coenzyme to the electrodes by immobilising flavin through semiconducting side chains, at certain selected positions, to electrodes such as graphite. Based on these studies, we have immobilisedfad on graphite electrodes. The chemical steps involve creating active centres on graphite which are reacted withfad to form covalent linkages between the electrode and the coenzyme. Cyclic voltamograms of the modified electrode show thatfad is active and undergoes the expected redox cycles. We hope that such electrodes will form suitable bioanodes forfad-linked enzymatic reactions.